You can control the page setup paramaters of your PowerPoint presentation by selecting [File] ... [Page Setup]. The page window (shown below) will be displayed.
Tips
PowerPoint can be used to create cover pages for reports, etc. by setting the Page Orientation to Portrait.
or maybe you want your slides to be vertical (Portrait).
and, this is where you set PowerPoint for the specific type of presentation that you are creating (e.g. On Screen, Letter Paper, A4 Paper, 35mm Slides, Overheads, etc.).